Photoflash lamp

ABSTRACT

A photoflash lamp of the percussive type in which the primer thereof comprises a metal tube and a charge of fulminating material on a wire anvil supported therein. The wire anvil is an alloy of iron, nickel and chromium and it is chemically etched to promote better adhesion and reduce flaking of the coating of fulminating material thereon and it is flame or hot air passivated so that long term stability of the fulminating material is realized.

United States Patent Armstrong et al.

[ 1 Nov. 11, 1975 1 1 PHOTOFLASH LAMP [75] Inventors: Donald E. Armstrong; Stephen V.

Brown; John W. Shaffer, all of Williamsport, Pa.

[73] Assignee: Sylvania Electric Products Inc.,

Danvers, Mass.

[22] Filed: July 19, 1974 [21] Appl. No.: 489,969

Related US. Application Data [63] Continuation of Ser. No. 887.005. Dec. 22. 1969,

abandoned.

[52] US. Cl. 431/93 [51] Int. Cl. F2lk 5/02 [58] Field of Search 431/93, 94

[56] References Cited UNITED STATES PATENTS 2.199.857 5/1940 Pipkin 431/94 2.658.845 11/1953 Barker 156/23 2.771.765 11/1956 Arnott et a1. 431/95 2944917 7/1960 Cahne 117/49 3.521.983 7/1970 Fink et a1 431/93 Prinmry E.\'anzinerCarroll B. Dority, Jr. Attorney. Agent, or FirmEdward J. Coleman 5 7 ABSTRACT A photoflash lamp of the percussive type in which the primer thereof comprises a metal tube and a charge of fulminating material on a wire anvil supported therein. The wire anvil is an alloy of iron. nickel and chromium and it is chemically etched to promote better adhesion and reduce flaking of the coating of fulminating material thereon and it is flame or hot air passivated so that long term stability of the fulminating material is realized.

3 Claims, 1 Drawing Figure US. Patent Nov. 11, 1975 DONALD E. ARMSTRONG STEPHEN V. BROWN JOHN W.SHAFFER INVENTO s W C ATTORNEY PHOTOFLASH LAMP I This is a continuation of application Ser. No. 887,005, filed Dec. 22, I969, now abandoned.

This invention relates to the manufacture of photoflash lamps and more particularly to those of the percussive type.

Generally speaking a percussive-type photoflash lamp comprises an hermetically sealed, lighttransmitting envelope containing a sourceof actinic light and having a primer secured there-to. More particularly, the percussive-type photoflash lamp may comprise a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible such as shredded zirconium foil and a combustion-supporting gas such as oxygen. The primer comprises a metal tube and a charge of fulminating material on a wire anvil supported therein. Operation of the lamp is initiated by an impact onto the tube of the primer to cause deflagration of the fulminating material on the wire anvil up through the tube to ignite the combustible disposed in the lamp envelope.

The fulminating material generally comprises a mixture of red phosphorus, potassium chlorate and a powdered metal such as zirconium. It must be extremely sensitive to impact ignition to insure high lamp reliability of flashing with the desirably-low impact energies delivered by the firing mechanism. At the same time,

the metal tube of the primer is thin-walled and soft so as to minimize the required impact and afford maximum lamp reliability. Application of a coating of fulminating material to a wire anvil may be effected by dipping the wire into a liquid suspension thereof. The wire used for the anvils may be an alloy of iron, nickel and chromium.

Early in the development of percussive-type photoflash lamps it was found that the fulminating material tended to flake off of the smooth metal surface of the anvil wire. These loose flakes of fulminating material in a finished lamp often caused accidental lamp ignitions prompted by vibration. In addition, the reliability of ignition by intentional impact is lowered because fulminating material is sometimes missing from the impact area.

One suggestion to overcome this problem was to provide the anvil wire with a rough surface by oxidizing the chromium-containing wire in an atmosphere of wet hydrogen. Such treatment forms a mossy coating of chromium oxide which promotes excellent adhesion of the fulminating material. Although this technique worked well on a laboratory scale, it is not readily adapted to a production operation on automated equipment. The oven time required for wet hydrogen oxidation is so long as to make treatment of a continuous length of wire impractical. Short pieces of wire, cut to the proper length first and then treated by a batch process, can be surface-roughened by this method. The automatic feeding and forming of such small pieces to the necessary dimensional tolerances is a formidable process. It is preferable to form the head and/or lobes first and then cut the wire to the desired length. Another difficulty is that in the batch process the cut lengths of wire tend to bond together at points of contact during treatment. Because the chromium oxide formed is very hard and abrasive, the tools that form the head and lobes would have an impractical short life. If the wire forming .tive from the standpoint of fulminating material adheis done prior to the wet hydrogen treatment, then the cut pieces of wire must be fed into the machine in a specific orientation. Automation of this operation and the integration of it into a high speed, mass production system would be both difficult and quite expensive.

, Another suggestion for providing the anvil wire with sion than is that obtained by the wet hydrogen process. It is more difficult to hold the wire diameter to the necessary close tolerances in a sand blasting process as compared to wet hydrogen surface oxidation.

In view of the foregoing, one of the principal objects of this invention is to providewire anvils for percussivetype photoflash lamps with a controlled surface roughness to promote good adhesion of the fulminating material thereon.

Another object is to provide these wire anvils with a chemically passivated surface so that long term stability of the fulminating material is realized.

A further object is to provide wire anvils for percussive-type photoflash lamps that may be readily fabricated and handled on automated manufacturing equipment.

Further objects, advantages and features are obtained, in accordance with the principles of this invention, by chemically etching the wire and then passivating it by a flame or hot air oxidizing process.

In the accompanying drawing, the single FIGURE is a sectional elevational view of a percussive-type photoflash lamp having a wire anviluof the type to which this invention is directed. The lamp comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constricted at one end to define an exhaust tip 4 and shaped to define a seal 6 about a primer 8 at the other end thereof. The primer 8 comprises a metal tube 10, a wire anvil l2 and a charge of fulminating material 14. By way of example, the fulminating material may comprise about 20% each of boron and zirconium, about 29% each of phosphorus and potassium chlorate and a little less then 2% hydroxyethyl cellulose. A combustible such as filamentary zirconium 16 and a combustion-supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered within the tube 10 and held in place by a crimp 18 just above the head 20 of the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial within the primer tube 10 and insuring clearance between the fulminating material 14 and the inside wall of the tube 10. A refractory bead 24, fused to the wire anvil 12 just above the inner mouth of the primer tube 10, eliminates burnthroughs and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer tube.

In order to promote better adhesion of the fulminating material 14 on the wire anvil l2 and to reduce flaking, the wire surface was chemically etched. Quite surprisingly, the energy required for reliable flashing of lamps with rough-surfaced anvil wire was lower than that for lamps with smooth-surfaced anvils. Conversely, at equal impact energy, higher lamp flashing reliability was obtained when the anvil had a rough surface. This effect has later been attributed to a tendency for the fulminating material to slide out of the impact zone when a smooth metal surface is present. A rough anvil surface was also found to promote more uniform wetting by the fluid fulminating material and resulted in an improved coating thickness uniformity.

In order to promote improved storage stability of the percussive-type photoflash lamps, the etched wire surface of the anvil wire is passivated by a flame or hot air oxidizing process. Such treatment is very rapid and suitable for production of rough-surfaced passivated wire in continuous spooled lengths that can be fed directly into automated production equipment. Flame or hot air oxidation forms a thin, adherent protective oxide coating on the rough etched surface. This surface is more inert toward the phosphorus-containing fulminating material than is an unoxidized chemically etched surface and thus long term stability of the fulminating material is realized.

As is readily appreciated by those skilled in the art there are many etch solutions for stainless steels and related materials described in the literature. By way of example, we have found that satisfactory results may be obtained with a solution comprising equal parts by weight of water, concentrated hydrochloric acid and ferric chloride hexahydrate. Etching is achieved by immersion of the wire in the etch solution for a controlled period of time, such as about one minute, for example. After etching the wire is rinsed free of acid in water. The clean reactive etched surface is then passivated by pulling the wire through either a flame or an electrically heated tube furnace. In essence, the wire is merely heated long enough to cause discoloration of the surface there. In practice, in addition to the advantage of improved storage stability obtained with passivated wire, it has been found that improved adhesion of head 24 is also obtained. Prior to such oxidation of the wire surface, the beads sometimes shattered off of the anvil wire during striker impact against the metal tube. This is apparently a vibration-initiated breaking of the bead. Such bead failure can contribute to lamp explosion or metal tube burnthrough during flash.

What we claim is:

1. A photoflash lamp comprising:

an hermetically sealed, light-transmitting envelope;

a quantity of filamentary combustible material located within said envelope;

a combustion-supporting gas in said envelope; and,

a primer secured to and extending from one end of said envelope and in communication with the interior thereof, said primer including a wire anvil having a rough etched surface with a thin, adherent oxide coating thereon and a coating of percussionsensitive fulminating material on a portion of said oxide coated, rough etched surface of the wire anvil.

2. The lamp of claim 1 wherein said wire anvil has a chemically etched surface whereby the adhesion and coating uniformity of said fulminating material on said wire anvil is improved, which results in a lower energy requirement for flashing the lamp and improved lamp flashing reliability.

3. The lamp of claim 2 wherein the etched surface of said wire anvil has an oxide coating provided by chemically passivating said wire anvil by a flame or hot air oxidizing process whereby said etched surface is rendered more inert toward said coating or fulminating material to thereby improve the storage stability of said lamp. 

1. A photoflash lamp comprising: an hermetically sealed, light-transmitting envelope; a quantity of filamentary combustible material located within said envelope; a combustion-supporting gas in said envelope; and, a primer secured to and extending from one end of said envelope and in communication with the interior thereof, said primer including a wire anvil having a rough etched surface with a thin, adherent oxide coating thereon and a coating of percussion-sensitive fulminating material on a portion of said oxide coated, rough etched surface of the wire anvil.
 2. The lamp of claim 1 wherein said wire anvil has a chemically etched surface whereby the adhesion and coating uniformity of said fulminating material on said wire anvil is improved, which results in a lower energy requirement for flashing the lamp and improved lamp flashing reliability.
 3. The lamp of claim 2 wherein the etched surface of said wire anvil has an oxide coating provided by chemically passivating said wire anvil by a flame or hot air oxidizing process whereby said etched surface is rendered more inert toward said coating or fulminating material to thereby improve the storage stability of said lamp. 